Problem 77
The complex ion \(\left[\mathrm{Co}\left(\mathrm{CO}_{3}\right)_{3}\right]^{3-},\) an octahedral complex with bidentate carbonate ions as ligands, has one absorption in the visible region of the spectrum at \(640 \mathrm{nm}\). From this information, (a) Predict the color of this complex and explain your reasoning. (b) Is the carbonate ion a weak- or strong-field ligand? (c) Predict whether \(\left[\mathrm{Co}\left(\mathrm{CO}_{3}\right)_{3}\right]^{3-}\) will be paramagnetic or diamagnetic.
Problem 80
A manganese compound has the formula \(\mathrm{Mn}(\mathrm{CO})_{x}\left(\mathrm{CH}_{3}\right)_{y}\) To find the empirical formula of the compound, you burn 0.225 g of the solid in oxygen and isolate \(0.283 \mathrm{g}\) of \(\mathrm{CO}_{2}\) and \(0.0290 \mathrm{g}\) of \(\mathrm{H}_{2} \mathrm{O} .\) What is the empirical formula for the compound? That is, what are the values of \(x\) and \(y ?\)
Problem 81
Nickel and palladium both form complexes of the general formula \(\mathrm{M}\left(\mathrm{PR}_{3}\right)_{2} \mathrm{Cl}_{2}\). (The ligand \(\mathrm{PR}_{3}\) is a phosphine such as \(\mathrm{P}\left(\mathrm{C}_{6} \mathrm{H}_{5}\right)_{3},\) triphenylphosphine. It is a Lewis base. The nickel( II) compound is paramagnetic whereas the palladium(II) compound is diamagnetic. (a) Explain the magnetic properties of these compounds. (b) How many isomers of each compound are expected?
Problem 85
Two different coordination compounds containing one cobalt(III) ion, five ammonia molecules, one bromide ion, and one sulfate ion exist. The dark violet form (A) gives a precipitate upon addition of aqueous \(\mathrm{BaCl}_{2}\). No reaction is seen upon addition of aqueous \(\mathrm{BaCl}_{2}\) to the violet- red form \((\mathrm{B})\) Suggest structures for these two compounds, and write a chemical equation for the reaction of (A) with aqueous \(\mathrm{BaCl}_{2}\).
Problem 87
A 0.213 -g sample of uranyl(VI) nitrate, \(\mathrm{UO}_{2}\left(\mathrm{NO}_{3}\right)_{2},\) is dissolved in \(20.0 \mathrm{mL}\) of \(1.0 \mathrm{M}\) \(\mathrm{H}_{2} \mathrm{SO}_{4}\) and shaken with Zn. The zinc reduces the uranyl ion, \(\mathrm{UO}_{2}^{2+},\) to a uranium ion, \(\mathrm{U}^{n+}\). To determine the value of \(n,\) this solution is titrated with \(\mathrm{KMnO}_{4} .\) Permanganate is reduced to \(\mathrm{Mn}^{2+}\) and \(\mathrm{U}^{n+}\) is oxidized back to \(\mathrm{UO}_{2}^{2+}\) (a) In the titration, \(12.47 \mathrm{mL}\) of \(0.0173 \mathrm{M} \mathrm{KMnO}_{4}\) was required to reach the equivalence point. Use this information to determine the charge on the ion \(\mathrm{U}^{n+}\). (b) With the identity of \(\mathrm{U}^{n+}\) now established, write a balanced net ionic equation for the reduction of \(\mathrm{UO}_{2}^{2+}\) by zinc (assume acidic conditions). (c) Write a balanced net ionic equation for the oxidation of \(\mathrm{U}^{n+}\) to \(\mathrm{UO}_{2}^{2+}\) by \(\mathrm{MnO}_{4}^{-}\) in acid.
Problem 88
Fireworks contain \(\mathrm{KClO}_{3}\). To analyze a sample for the amount of \(\mathrm{KClO}_{3}\) a chemist first reacts the sample with excess iron(II), $$\begin{array}{r}\mathrm{ClO}_{3}^{-}(\mathrm{aq})+6 \mathrm{Fe}^{2+}(\mathrm{aq})+6 \mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq}) \longrightarrow \\\\\mathrm{Cl}^{-}(\mathrm{aq})+9 \mathrm{H}_{2} \mathrm{O}(\ell)+6 \mathrm{Fe}^{3+}(\mathrm{aq})\end{array}$$ and then titrates the resulting solution with \(\mathrm{Ce}^{4+}\) [in the form of \(\left.\left(\mathrm{NH}_{4}\right)_{2}\mathrm{Ce}\left(\mathrm{NO}_{3}\right)_{6}\right]\) $$\mathrm{Fe}^{2+}(\mathrm{aq})+\mathrm{Ce}^{4+}(\mathrm{aq}) \longrightarrow \mathrm{Fe}^{3+}(\mathrm{aq})+\mathrm{Ce}^{3+}(\mathrm{aq}) $$ to determine the quantity of iron(II) that did not react with \(\mathrm{ClO}_{3}^{-}\). (This is referred to as a "back titration." Suppose a 0.1342-g sample of a firework was treated with 50.00 mL. of \(0.0960 \mathrm{M} \mathrm{Fe}^{2+}\) The unreacted \(\mathrm{Fe}^{2+}\) ions then required \(12.99 \mathrm{mL}\) of \(0.08362 \mathrm{M} \mathrm{Ce}^{4+} .\) What is the weight percent of \(\mathrm{KClO}_{3}\) in the original sample?
Problem 90
In this question, we explore the differences between metal coordination by monodentate and bidentate ligands. Formation constants, \(K_{t}\), for \(\left[\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{6}\right]^{2+}(\mathrm{aq})\) and \(\left[\mathrm{Ni}(\mathrm{en})_{3}\right]^{2+}(\mathrm{aq})\) are as follows: \(\mathrm{Ni}^{2+}(\mathrm{aq})+6 \mathrm{NH}_{3}(\mathrm{aq}) \longrightarrow\left[\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{6}\right]^{2+}(\mathrm{aq}) \quad K_{\mathrm{f}}=10^{8}\) \(\mathrm{Ni}^{2+}(\mathrm{aq})+3 \mathrm{en}(\mathrm{aq}) \longrightarrow\left[\mathrm{Ni}(\mathrm{en})_{3}\right]^{2+}(\mathrm{aq})\) \(K_{f}=10^{18}\) The difference in \(K_{f}\) between these complexes indicates a higher thermodynamic stability for the chelated complex, caused by the chelate effect. Recall that \(K\) is related to the standard free energy of the reaction by \(\Delta_{r} G^{\circ}=-R T \ln K\) and \(\Delta_{r} G^{\circ}=\) \(\Delta_{r} H^{\circ}-T \Delta_{r} S^{\circ} .\) We know from experiment that \(\Delta_{t} H^{\circ}\) for the \(\mathrm{NH}_{3}\) reaction is \(-109 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn}\) and \(\Delta_{i} H^{\circ}\) for the ethylenediamine reaction is \(-117 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn} .\) Is the difference in \(\Delta_{r} H^{\circ}\) suffi- cient to account for the \(10^{10}\) difference in \(K_{f} ?\) Comment on the role of entropy in the second reaction.
